Distribution and Abundance of Dungeness Crab and Crangon Shrimp and Dredging-Related Mortality of Invertebrates and Fish in Grays Harbor, Washington

摘要

The impacts of widening and deepening the existing navigation channel in Grays Harbor on Dungeness crab, Crangon shrimp and fish was investigated. The spatial and temporal distribution of these organisms was studied using an otter trawl and ring nets, and the uptake of organisms by dredges was estimated from samples collected on working hopper and pipeline dredges. Mean crab trawl catch per unit effort over the 14 month sampling period ranged from 7.56 crabs/100 sq m at South Reach to 1.19 crabs/100 sq m at South Channel; generally decreasing with increasing distance upriver from the harbor mouth and decreasing salinity. Crabs were most abundant in spring and least abundant in summer. Diel migrations were evident and dependent upon tidal level, light and salinity. Annual mean crab density was greater in the channel than on the flats. Crabs generally changed their diet with age from one consisting of molluscs and crustaceans (especially Crangon shrimp) to fish. Tomcod, Longfin smelt, Staghorn sculpin and English sole were the most frequently caught fish species. South Reach consistently had the highest densities of fish and highest number of fish species. Crangon franciscorum was the dominant species of Crangonid shrimp in Grays Harbor and its population reached a high seasonal peak in the inner Harbor from May through August. Abundances of all Crangonid species varied at sites with season, tidal level and salinity. Total shrimp population estimates in Grays Harbor were 24.8 million in summer and 7.4 million in winter.